The problem of air in a disposable liner of nursing bottles has been recognized for some time. The prior art disclose devices which are used to eliminate air from the liner. For example, the prior art disclose the use of plungers, such as those disclosed in U.S. Pat. No. 5,524,783 to Popoff, U.S. Pat. No. 4,880,125 to LeBleau, and U.S. Pat. No. 3,648,873 to Grobbel. The end of the plunger is used to mechanically collapse the liner toward a nipple on the nursing bottles which causes a decrease in volume of the liner. As the liquid in the liner moves upward in response to the mechanical pressure from the plunger, the air in the liner is expelled through the nipple. A similar device is disclosed in U.S. Pat. No. 4,176,745 to Miller that has a pneumatic member (12) that applies a force to a liner to expel air in the liner.
A problem with these devices is that, if the plunger or pneumatic member is removed, there is nothing to prevent the liner from re-expanding and air being reintroduced into the liner. This necessitates that the liner again be collapsed to expel the air before the nursing bottle is used to feed an infant.
Many nursing bottles use disposable liners. These liners provide for easy cleaning as they are simply thrown away after use and replaced. Many of these nursing bottles have apertures in the bottoms to allow air into the bottle as the baby takes liquid from the nursing bottle. This allows the pressure around the liner to be equal to the pressure outside of the nursing bottle. Examples of these types of nursing bottles are U.S. Pat. No. 2,987,209 to Leonard and U.S. Pat. No. 2,846,103 to Maxwell.
Still other nursing bottles do not use liners, but employ a valve on the bottom of the bottle. Examples include U.S. Pat. No. 3,768,682 to Myers et al., U.S. Pat. No. 3,292,808 to Greene, and U.S. Pat. No. 3,511,407 to Palma. The valve allows air to enter the nursing bottle to replace the volume of liquid that is consumed by the infant during feeding. The valve opens when the pressure in the bottle is less than the pressure outside of the nursing bottle. The valve prevents the liquid in the nursing bottle from leaking when the nursing bottle is in the upright position.